1. Field of the Invention
The present invention relates to a projection type image displaying apparatus in which light reflected by a reflection type optical spatial modulator element, such as a digital mirror device (DMD(trademark), simply called DMD hereinafter) chip, is projected onto a screen to display am image included in the light.
2. Description of Related Art
A projection type image displaying apparatus is generally called a digital light processor (DLP) and denotes a projector using a DMD chip. In the DMD chip, a large number of micro-mirrors respectively having a size of 16 xcexcm square are disposed in a two-dimensional matrix shape at pitches (or intervals) of 17 xcexcm. Each micro-mirror of the DMD chip is inclined by an angle of +10 degrees so as to be set to an on-state and is inclined by an angle of xe2x88x9210 degrees so as to be set to an off-state. In this case, a flux of light reflected by the micro-mirror in the on-state propagates in an on-direction, and a flux of light reflected by the micro-mirror in the off-state propagates in an off-direction. Therefore, a flux of light reflected on the micro-mirror is switched from the on-direction (or the off-direction) to the off-direction (or the on-direction).
In this case, the position relation between the DMD chip and a projection lens is set so as to make a flux of light reflected by each micro-mirror in the on-state pass through an entrance pupil of the projection lens, and each flux of light passing through the entrance pupil of the projection lens reaches a pixel of a screen. Also, the position relation between the DMD chip and a projection lens is set so as to make a flux of light reflected by each micro-mirror in the off-state pass out of the entrance pupil of the projection lens, and no light reaches the screen. Therefore, a flux of light reflected by each micro-mirror in the on-state brightens the corresponding pixel of the screen, and a flux of light reflected by each micro-mirror in the off-state does not brighten the corresponding pixel of the screen. When fluxes of light are incident on the micro-mirrors of the DMD chip respectively, fluxes of outgoing light reflected by the micro-mirrors in the on-state have image information. The fluxes of outgoing light having the image information pass through the projection lens and are projected onto the screen. Therefore, an image is displayed on the screen according to the image information.
FIG. 9 is a view showing the configuration of a conventional image displaying apparatus. FIG. 10A shows the position relation between a total internal reflection (TIR) prism and a DMD chip shown in FIG. 9. FIG. 10B shows fluxes of light incident on micro-mirrors of a DMD chip shown in FIG. 9.
In FIG. 9, 110 indicates a high pressure mercury lamp (or a lighting source system) for generating light and radiating parallel light. 120 indicates a plurality of condenser lenses (or the lighting source system) for converging the parallel light radiated from the high pressure mercury lamp 110 onto a focal point. 130 indicates a rod integrator (or the lighting source system) for receiving the converged light output from the condenser lenses 120 and outputting a plurality of fluxes of light having a uniform intensity distribution. 140 indicates a relay lens system for relaying the fluxes of light output from the rod integrator 130. A diaphragm 141 having an aperture is placed in the relay lens system 140. The fluxes of light output from the rod integrator 130 are deformed in the diaphragm 141. 160 indicates a DMD chip. 150 indicates a total internal reflection (TIR) prism (or a total reflection prism) for totally reflecting the fluxes of light received from the relay lens system 140 so as to send the fluxes of light to the DMD chip 160 and transmitting the fluxes of light reflected by the DMD chip 160. 170 indicates a projection lens (or a projecting optical system) for projecting the fluxes of light, which are reflected by the DMD chip 160 and transmitted through the TIR prism 150, onto a screen. Here, the screen of the conventional image displaying apparatus is omitted in FIG. 9.
Also, in FIG. 10A, 151 indicates a surface (hereinafter, called an opposite-to-DMD surface) of the TIR prism 150. The opposite-to-DMD surface 151 is opposite to the DMD chip 160. 161 indicates a glass cover plate of the DMD chip 160. 162 indicates each of a large number of micro-mirrors of the DMD chip 160. 163 indicates a substrate of the DMD chip 160. The substrate 163 of the DMD chip 160 is placed so as to be parallel to the opposite-to-DMD surface 151 of the TIR prism 150. Also, the glass cover plate 161 is placed so as to be parallel to a flat surface of the substrate 163.
Next, an operation of the conventional image displaying apparatus will be described below.
Parallel light is emitted from the high pressure mercury lamp 110 and is converged onto a focal point of the condenser lens 120. An incident end face of the rod integrator 130 is placed at the focal point of the condenser lens 120. Therefore, converged light output from the condenser lens 120 is incident on the rod integrator 130. In the rod integrator 130, a plurality of fluxes of light are produced from the converged light, intensities of the fluxes of light are equalized, and the fluxes of light having an almost uniform intensity distribution are output from an outgoing end face of the rod integrator 130.
Thereafter, the fluxes of light output from the rod integrator 130 pass through the relay lens system 140 having the diaphragm 141 and are incident on the TIR prism 150. The fluxes of light incident on the TIR prism 150 are totally reflected on a face of the TIR prism 150 and pass through the opposite-to-DMD surface 151 and the glass cover plate 161 in that order, and the fluxes of light are incident on the DMD chip 160. In the DMD chip 160, each flux of incident light is reflected on the corresponding micro-mirror 162 set to either the on-state or the off-state and propagates in the on-direction or off-direction as a flux of outgoing light. A plurality of fluxes of outgoing light reflected on the micro-mirrors 162 of the on-state and propagating in the on-direction are returned from the DMD chip 160 to the TIR prism 150, pass through the projection lens 170 and are projected onto a screen (not shown). Therefore, an image is displayed on the screen.
Because the conventional image displaying apparatus has the above-described configuration, a portion of the light totally reflected on a face of the TIR prism 150 is reflected on the opposite-to-DMD surface 151 placed at a boundary surface between the TIR prism 150 and the air, and the portion of the light undesirably passes through the projection lens 170. Also, another portion of the light totally reflected on a face of the TIR prism 150 is reflected on a boundary surface between the glass cover plate 161 and the air, and the portion of the light undesirably passes through the projection lens 170. Therefore, the portions of the light are projected on the screen, and a problem has arisen that a contrast of the image displayed on the screen deteriorates due to the portions of the light.
This problem will be described in detail with reference to FIG. 10A and FIG. 10B.
In cases where rays of light other than light reflected on the micro-mirrors 162 of the on-state pass through the entrance pupil of the projection lens 170, a contrast between white and black in the image displayed on the screen deteriorates due to the rays of light. The rays of light other than light reflected on the micro-mirrors 162 of the on-state are derived from light reflected on a top surface of the glass cover plate 161, light reflected on a bottom surface of the glass cover plate 161 and light reflected on the opposite-to-DMD surface 151 of the TIR prism 150.
As shown in FIG. 10A, C1 denotes rays of specular reflection light. The rays of specular reflection light C1 are obtained by specularly reflecting a portion of light entering the TIR prism 150 on the top surface of the glass cover plate 161 opposite to the TIR prism 150. C2 denotes rays of specular reflection light. The rays of specular reflection light C2 are obtained by specularly reflecting a portion of light entering in the TIR prism 150 on the bottom surface of the glass cover plate 161 opposite to the DMD chip 160. C3 denotes rays of specular reflection light. The rays of specular reflection light C3 are obtained by specularly reflecting a portion of light entering in the TIR prism 150 on the opposite-to-DMD surface 151 of the TIR prism 150. Therefore, the rays of specular reflection light C1 and C2 are generated on the boundary surface between the glass cover plate 161 and the air due to a difference in refractive index between the glass cover plate 161 and the air, and the rays of specular reflection light C3 are generated on the boundary surface between the TIR prism 150 and the air due to a difference in refractive index between the TIR prism 150 and the air.
When no antireflection film is used for the TIR prism 150 or the glass cover plate 161, reflectivity of light passing through each boundary surface is equal to almost 4%. Also, even though an antireflection film is used for the TIR prism 10 and the glass cover plate 161, because the spectrum of the light has a wide spectral range corresponding to white light and because the light has a wide incident angle to each micro-mirror 162, reflectivity of the light is only lowered to 0.5 to 1% at the best. Therefore, the rays of the specular reflection light C1, C2 and C3 are inevitably generated and function as stray light.
In particular, as shown in FIG. 10B, each micro-mirror 162 of the DMD chip 160 is illuminated with a flux of light having a diverging angle xcex8. Therefore, to efficiently illuminate the DMD chip 160 with the fluxes of light, it is required to illuminate the DMD chip 160 with fluxes of light converged in the relay lens system 140 at a large diverging angle and to project the fluxes of light reflected on the micro-mirrors 162 of the on-state onto the screen through the projection lens 170 having a large relative aperture (or a small F-number). In this case, because the rays of specular reflection light C1, C2 and C3 overlap with a portion of each flux of light reflected on the corresponding micro-mirror 162 of the on-state, the rays of specular reflection light C1, C2 and C3 pass through the entrance pupil of the projection lens 170 having a large relative aperture.
The rays of specular reflection light C1 incident on the projection lens 170 of the conventional image displaying apparatus are shown in FIG. 11, and the rays of specular reflection light C3 incident on the projection lens 170 of the conventional image displaying apparatus are shown in FIG. 12. The constituent elements, which are the same as those shown in FIG. 9, are indicated by the same reference numerals as those of the constituent elements shown in FIG. 9.
Also, FIG. 13A shows a flux of incident light incident on a micro-mirror set to the on-state and a flux of outgoing light reflected on the micro-mirror, and FIG. 13B shows a flux of incident light incident on a micro-mirror set to the off-state and a flux of outgoing light reflected on the micro-mirror. FIG. 14 shows an angular distribution (xcex8x, xcex8y) of a flux of incident light, an angular distribution (xcex8x, xcex8y) of a flux of outgoing light reflected on one micro-mirror 162 of the on-state, an angular distribution (xcex8x, xcex8y) of the specular reflection light C1, C2 and C3 and an angular distribution (xcex8x, xcex8y) of a flux of outgoing light reflected on one micro-mirror 162 of the off-state.
In FIG. 13A, and FIG. 13B, one micro-mirror 162 is set to the on-state by inclining the micro-mirror 162 counter-clockwise by 10 degrees with respect to a flat surface of the substrate 163 of the DMD chip 160, and the micro-mirror 162 is set to the off-state by inclining the micro-mirror 162 clockwise by 10 degrees with respect to a flat surface of the substrate 163 of the DMD chip 160. A flux of incident light Fin incident on the micro-mirror 162 has a diverging angle of xcex8=16.4 degrees. This diverging angle of the flux of incident light Fin corresponds to an F-number (F =1/(2xc3x97tan xcex8)) of the relay lens system 140 set to F=1.7. The flux of incident light Fin is incident on the micro-mirror 162 at an incident angle of 20 degrees to the DMD chip 160. That is, a principal ray Rin of the flux of incident light Fin makes an angle of 20 degrees to a normal NO of the DMD chip 160. The flux of incident light Fin is deformed in the diaphragm 141 so as not to overlap with a flux of outgoing light Fout reflected on the micro-mirror 162.
In FIG. 14, AD1 denotes an angular distribution of the flux of incident light Fin, AD2 denotes an angular distribution of the flux of outgoing light Fout reflected on the micro-mirror 162 of the on-state, AD3 denotes an angular distribution of the rays of specular reflection light C1, C2 and C3, and AD4 denotes an angular distribution of the flux of outgoing light Fout reflected on the micro-mirror 162 of the off-state. EP denotes an entrance pupil of the projection lens 170. The entrance pupil EP is formed in a circular shape having a radius of 16.4 degrees.
The angular distribution AD1 of the flux of incident light Fin is formed in a D shape by straightly cutting off a right portion of a circular-shaped flux. Therefore, each of the angular distributions AD2 to AD4 of the light fluxes obtained by reflecting the flux of incident light Fin is formed in the D shape.
When the flux of incident light Fin is incident on the micro-mirror 162 set to the on-state, the flux of outgoing light Fout reflected on the micro-mirror 162 propagates in the on-direction. In this case, a principal ray Rout1 of the flux of outgoing light Fout propagates in parallel to the normal NO of the DMD chip 160. Therefore, as shown in FIG. 14, the flux of outgoing light Fout reflected on the micro-mirror 162 of the on-state has an angular distribution centering around (xcex8x, xcex8y)=(0,0). Here, the normal NO of the DMD chip 160 is parallel to a Z axis, xcex8x denotes an angle between the propagation direction of light and the normal NO of the DMD chip 160 on an X-Z plane, and xcex8y denotes an angle between the propagation direction of light and the normal NO of the DMD chip 160 on a Y-Z plane.
Also, when the flux of incident light Fin is incident on the micro-mirror 162 set to the off-state, the flux of outgoing light Fout reflected on the micro-mirror 162 propagates in the off-direction. In this case, a principal ray Rout2 of the flux of outgoing light Fout propagates in a direction making an angle of 40 degrees to the normal NO of the DMD chip 160. Therefore, as shown in FIG. 14, the flux of outgoing light Fout reflected on the micro-mirror 162 of the off-state has an angular distribution centering around (xcex8x, xcex8y)=(40 degrees, 0). Also, because the rays of specular reflection light C1, C2 and C3 are obtained by specularly reflecting the flux of incident light Fin on a plane parallel to the flat surface of the substrate 163 of the DMD chip 160, as shown in FIG. 14, the rays of specular reflection light C1, C2 and C3 have an angular distribution centering around (xcex8x, xcex8y)=(20 degrees, 0).
To receive the flux of outgoing light Fout reflected on the micro-mirror 162 of the on-state in the projection lens 170, the projection lens 170 is, for example, set to the F-number of F=1.7 to have the entrance pupil EP in which the flux of outgoing light Fout reflected on the micro-mirror 162 of the on-state is entered. In this case, though the flux of outgoing light Fout reflected on the micro-mirror 162 of the on-state passes through the entrance pupil EP of the projection lens 170, a portion of the rays of specular reflection light C1, C2 and C3 undesirably pass through the entrance pupil EP of the projection lens 170. Therefore, a contrast of an image displayed on the screen according to the flux of outgoing light Fout reflected on the micro-mirror 162 of the on-state deteriorates due to the portion of the rays of specular reflection light C1, C2 and C3 undesirably passing through the entrance pupil EP of the projection lens 170.
Also, because each micro-mirror 162 is inclined with respect to the flat surface of the substrate 163 of the DMD chip 160, an area not covered with any inclined micro-mirror 162 exists on the substrate 163 of the DMD chip 160. In this case, a portion of the incident light Fin passes though the area of the substrate 163 not covered with any inclined micro-mirror 162 and is undesirably scattered or reflected on the substrate 163 of the DMD chip 160. The portion of the incident light Fin scattered or reflected on the substrate 163 of the DMD chip 160 undesirably passes through the projection lens 170 as stray light, and a contrast of the image deteriorates.
Also, an open space is preset between each pair of micro-mirrors 162 adjacent to each other. An area of the open spaces is almost equal to 10% of a total area of the substrate 163 of the DMD chip 160. Therefore, a portion of the incident light Fin passes though the open space between each pair of micro-mirrors 162 adjacent to each other and is undesirably scattered or reflected on the substrate 163 of the DMD chip 160. In this case, the portion of the incident light Fin scattered or reflected on the substrate 163 of the DMD chip 160 undesirably passes through the projection lens 170 as stray light, and a contrast of the image deteriorates.
An object of the present invention is to provide, with due consideration to the drawbacks of the conventional image displaying apparatus, an image displaying apparatus in which a contrast of a displayed image is improved.
The object is achieved by the provision of an image displaying apparatus including a reflection type optical spatial modulator element for receiving a plurality of fluxes of incident light from a lighting source system and outputting a plurality of fluxes of outgoing light including image information, and a projecting optical system for projecting a plurality of fluxes of outgoing light, which are output from the reflection type optical spatial modulator element and propagate in an on-direction, onto a screen to display an image on the screen according to the image information included in the fluxes of outgoing light. The reflection type optical spatial modulator element includes a substrate extending on a reference plane, a transparent cover plate extending in a specific direction not parallel to the reference plane of the substrate, and a plurality of micro-mirrors, disposed on the substrate and respectively inclined by an on-angle or an off-angle with respect to the reference plane of the substrate so as to be set to an on-state or an off-state, for reflecting the fluxes of incident light passing through the transparent cover plate as the fluxes of outgoing light to propagate each flux of outgoing light reflected on the micro-mirror of the on-state in the on-direction and to propagate each flux of outgoing light reflected on the micro-mirror of the off-state in an off-direction.
In the above configuration, because the transparent cover plate is disposed not to be parallel to the reference plane of the substrate, no specular reflection light generated on a surface of the transparent cover plate propagates in the on-direction. Therefore, no specular reflection light passes through the projecting optical system, and a contrast of the displayed image can be improved.
The object is also achieved by the provision of an image displaying apparatus including a total reflection prism having an opposite-to-modulator surface, a reflection type optical spatial modulator element disposed so as to be opposite to the opposite-to-modulator surface of the total reflection prism, receiving the fluxes of incident light output from the lighting source system through the total reflection prism and outputting a plurality of fluxes of outgoing light including image information, and a projecting optical system for projecting the fluxes of outgoing light, which are output from the reflection type optical spatial modulator element and propagate in an on-direction, onto a screen to display an image on the screen according to the image information included in the fluxes of outgoing light. The reflection type optical spatial modulator element includes a substrate, a transparent cover plate, a refractive index matching layer having a refractive index near to both the transparent cover plate and the total reflection prism and placed between the transparent cover plate and the opposite-to-modulator surface of the total reflection prism, and a plurality of micro-mirrors, disposed on the substrate and respectively inclined by an on-angle or an off-angle so as to be set to an on-state or an off-state, for receiving each flux of incident light through the refractive index matching layer and the transparent cover plate, and reflecting the fluxes of incident light as the fluxes of outgoing light to propagate each flux of outgoing light reflected on the micro-mirror of the on-state in the on-direction and to propagate each flux of outgoing light reflected on the micro-mirror of the off-state in an off-direction.
In the above configuration, because the refractive index matching layer is placed between the transparent cover plate and the opposite-to-modulator surface of the total reflection prism, no specular reflection light is generated due to a difference in refractive index between the transparent cover plate and the total reflection prism. Therefore, no specular reflection light passes through the projecting optical system, and a contrast of the displayed image can be improved.
The object is also achieved by the provision of an image displaying apparatus including a reflection type optical spatial modulator element for receiving the fluxes of incident light output from a lighting source system and outputting a plurality of fluxes of outgoing light including image information, and a projecting optical system for projecting the fluxes of outgoing light, which are output from the reflection type optical spatial modulator element and propagate in an on-direction, onto a screen to display an image on the screen according to the image information included in the fluxes of outgoing light. The reflection type optical spatial modulator element includes a transparent cover plate, a plurality of micro-mirrors, respectively inclined by an on-angle or an off-angle so as to be set to an on-state or an off-state, for reflecting the fluxes of incident light passing through the transparent cover plate as the fluxes of outgoing light to propagate each flux of outgoing light reflected on the micro-mirror of the on-state in the on-direction and to propagate each flux of outgoing light reflected on the micro-mirror of the off-state in an off-direction, and a substrate for supporting the micro-mirrors and preventing each flux of incident light, which passes through the transparent cover plate and is not incident on any micro-mirror, from going out to the projecting optical system.
In the above configuration, because the substrate prevents each flux of incident light, which passes through the transparent cover plate and is not incident on any micro-mirror, from going out to the projecting optical system, even though light passes through an open space between each pair of micro-mirrors adjacent to each other, the light incident on the substrate does not pass through the projecting optical system. Therefore, a contrast of the displayed image can be improved.